O CYRTIDAIO OF NORTH AMERICA 



Structural Characters 



Osten Sacken noted the fact that a considerable number of the 

 archaic forms occurred in the Eremochaeta, "survivals of bygone 

 zoological horizons" as he aptly terms them. The genera near 

 the Nemestrinidae in venation and with a long proboscis are the 

 oldest, one species of this type having been recently described by 

 Meunicr fi'om Baltic amber. In the Cyrtidae we have a family 

 which has been modified by parasitism; undoubtedly those genera 

 having a long proboscis and a complex wing venation are the 

 oldest forms and the others have become curiously degraded 

 by their mode of life. 



These very interesting flies vary in size; the smallest one 

 known to me being 2.5 millimeters long and the largest about 17 

 mm. They belong to the Orthorrhapha brachycera and are 

 devoid of bristles. The head is small and composed almost en- 

 tirely of the huge rounded eyes. Both sexes are holoptic or 

 nearly so, and the face is small and situated almost on the under 

 side of the head. There are usually three ocelli, but some forms 

 have two and the European Astomella none; Lasia ocelUger is 

 said to have one ocellus. The proboscis in one group is so small 

 as to be hardly visible (with the mouth opening closed by a 

 membrane in one genus), and in the others is long and slender. 

 The eyes may be hairy or bare, with all the facets equal. The 

 antennae are three jointed, although there are at times appar- 

 ently only two joints, the first being sunken in the head. The 

 antennae are usually short, close together at the base (in Pialea 

 grown together) , and in varying positions on the head ; thej^ may 

 be just below the ocelli on the vertex, in the middle of the head or 

 far down on the rim of the mouth. In one group the third joint 

 is short and with a long, thin apical arista; in another group 

 elongate and strap-shaped, and in Pterodontta with three apical 

 setae. 



The thoi'ax is humped and rounded and umch wider than the 

 head. In the Philopotinae the prothoracic lobes are abnormally 

 enlarged and meet above to form a shield on the prothorax. 

 The pubescence is very thick in some species, but there are never 

 any bristles. The scutellum is large, usually concealing the 

 metanotum. 



